@3.2.0 can't call webkit.messageHandlers.cordova_iab.postMessage

when I want to call webkit.messageHandlers.cordova_iab.postMessage on my webpage.htm, window.webkit is undefined, but it can work on @3.1.0 inappbrowser.....

so, I try to find reason, if I want to use post message, I have to do ...
var ref=window.open ('http://xxxx/mypage.htm')
// I must call this, so my page.htm can use webkit.messageHandlers....
ref.addEventListener('loadstone', function (){ ref.execJavaScript(';')});

Start with the reported calls in webpage.htm: window.webkit, webkit.messageHandlers.cordova_iab.postMessage, window.open, the loadstone listener, and ref.execJavaScript. Reproduce the difference between plugin versions 3.2.0 and 3.1.0 and determine why window.webkit is unavailable; done means postMessage works without the reported workaround or the limitation is documented.

Written by the indexing model from the issue text.